A digital-type protection control apparatus, an NCT (Network Computing Terminal), an electric power quality measurement apparatus, and the like are known as examples of control systems. In general, protection control of an electric power system is done by a digital-type protection control apparatus. The digital-type protection control apparatus receives a state quantity of an electric power system which changes every moment, and performs stabilization control and system protection control by finding changes in state of multiple pieces of equipment constituting the electric power system and abnormal situations such as an accident occurring in the multiple pieces of equipment. In particular, in recent years, digital-type protection control apparatuses having high-performance electronic devices such as a high-speed processing microprocessor and a large-capacity memory are employed, and their functions are improved.
As a digital-type protection control apparatus, various kinds of apparatuses have been developed in accordance with the contents of protection control mainly for electric power systems, and the various kinds of apparatuses are employed at required portions of the electric power systems. More specifically, a digital relay is also installed to protect an electric power system by separating a portion where an accident has occurred from the electric power system by detecting an accident (system accident) that has occurred in each piece of equipment (an electrical power transmission line, a transformer and the like) of the electric power system, and a monitoring control apparatus is also installed to control the connection configuration of the system.
Any one of these digital-type protection control apparatuses receives analog state quantities of currents and voltages of the electric power system, and performs various kinds of digital operational processing based on digital values converted by analog/digital conversion (hereinafter referred to as A/D conversion). In addition to the above, systems for performing various kinds of operations upon receiving the analog input quantities are as follows: various kinds of apparatuses such as a malfunctioning point locating apparatus (fault locator) for accurately locating a position of an accident point (malfunctioning point) on an electrical power transmission line, a system analyzing apparatus (oscillograph apparatus) for recording an oscillograph at a time of occurrence of an accident, and a measurement apparatus relating to electric power qualities such as harmonics and voltage sag (instantaneous drop of voltage) are installed.
Hereinafter, a digital-type protection control apparatus will be explained using an example of a digital relay for performing a protecting relay operation on an electric power system. FIG. 55 is a configuration diagram illustrating a basic configuration of a conventional digital relay for multiple inputs, which is an example of a conventional digital-type protection control apparatus. According to FIG. 55, a digital relay 1 includes an analog/digital conversion unit 2 for retrieving many analog state quantities (electric quantities) A-1 to A-n such as currents and voltages from an electric power system, which is a target of protection control, and converting the analog state quantities A-1 to A-n into digital data, a digital operation processing unit 3 for performing protection control operation based on state data digitalized by this analog/digital conversion unit 2, an input/output interface unit (I/O) 4 for performing interface processing related to data input/output to/from electric power system protection control apparatuses (protection control apparatuses) such as a circuit breaker and a protection relay, and a display device 14 such as an LED for displaying operation of the protection control apparatuses and the electric quantity data.
All constituent elements of this digital relay 1 (the analog/digital conversion unit 2, the digital operation processing unit 3, the input/output interface unit 4, and the display device 14) are connected to each other via a bus 5 in such a manner that they can transmit and receive data between each other.
The analog/digital conversion unit 2 includes n analog filters 6-1 to 6-n, for unnecessary frequency component removal, which are as many as the number of input electric quantities (A-1 to A-n), sampling hold circuits 7-1 to 7-n, for sampling, which correspond to the analog filters 6-1 to 6-n, respectively, a multiplexer 8 for selection output, and an A/D conversion device 9 for A/D conversion.
On the other hand, the digital operation processing unit 3 is constituted by a computer circuit. More specifically, the digital operation processing unit 3 includes a CPU 10 for execution of protection control operation processing, a random access memory (RAM) 11 for temporarily saving the electric quantity data and data generated during processing performed by the CPU 10, a read-only memory (ROM) 12 for saving a processing procedure (program) of protection control, and a nonvolatile memory (EEPROM) 13 for storing set points in a rewritable manner. The display device 14 is constituted by an LED and the like, and displays operations of the protection control apparatuses such as the circuit breaker and the electric quantity data saved in the RAM 11 by the processing of the CPU 10.
According to the digital relay 1 thus configured, each of the unnecessary frequency components (such as harmonic components other than the fundamental wave and direct current component) are removed by means of the analog filters 6-1 to 6-n from the n electric quantities A-1 to A-n retrieved in parallel from the electric power system, and thereafter, the n electric quantities A-1 to A-n are transmitted to the sampling hold circuits 7-1 to 7-n, where each of them are sampled as state values (instantaneous values) with a time interval (cycle) defined in advance.
The instantaneous values respectively sampled by the sampling hold circuits 7-1 to 7-n are sequentially and selectively output from a single output end via the multiplexer 8, and are transmitted to the A/D conversion device 9. Then, the instantaneous values transmitted to the A/D conversion device 9 are converted into digitalized electric quantity data by the A/D conversion device 9, and thereafter, the instantaneous values are sequentially output to the digital operation processing unit 3 via the bus 5. The electric quantity data which are sequentially output to the digital operation processing unit 3 are transferred to the RAM 11 in order and temporarily stored therein according to reading processing performed by the CPU 10 based on a protection control program stored in the ROM 12.
Then, based on the electric quantity data stored in the RAM 11, the set points of the protecting relay operation stored in the EEPROM 13, contact point information of external apparatuses such as circuit breakers retrieved via the input/output interface unit 4, and the like, the CPU 10 executes protection control operation processing (for example, digital filtering processing, amplitude value operation processing, effective value operation processing, phase difference operation processing, operation determining processing based on set points and the like) in accordance with a protection control program stored in the ROM 12.
The result obtained from the protection control operation processing performed by the CPU 10 as described above is output, by the processing performed by the CPU 10, to a protection control apparatus such as a circuit breaker via the input/output interface unit 4 as a protection control operation instruction such as a trip instruction (trip instruction) and a turn-on instruction to the external apparatus (the protection control apparatus) such as a circuit breaker, and the electric power system protection control operation {trip operation/turn-on operation (contact point open/close operation) and the like) is executed.
The electric quantity data stored in the RAM 11 are displayed as electric quantities by means of the display device 14 by display processing performed by the CPU 10. It should be noted that not only the digital relay but also other digital-type protection control apparatuses having protection control functions have substantially the same configuration as the digital relay 1 as explained above, although those digital-type protection control apparatuses are different in the protection control operation processing and the contents of protection control, and those digital-type protection control apparatuses are configured to perform similar operation processing.
In recent years, as the demand for electric power increases, apparatuses of an electric power system are distributed over a wider area, and accordingly, there are a larger number of control stations such as electric power stations and digital-type protection control apparatuses provided in these control stations for controlling equipment of such electric power system distributed over a wide area.
On the other hand, FIG. 56 is a configuration diagram when a digital protection control apparatus (digital relay) is arranged for equipment such as an electrical power transmission line and a bus wire of an electric power system. In FIG. 2, an electric power system is represented in a single-line diagram. As illustrated in FIG. 56, electrical power transmission lines 16A, 16B of an electric power system 15 are respectively provided with electrical power transmission line protection relays 1A, 1B which receive state quantities (electric power quantity such as currents and voltages) flowing in these electrical power transmission lines 16A, 16B and a bus wire 17 using transformers such as a measurement transformer 18A and a measurement transformer 18B and protect the electrical power transmission lines 16A, 16B by activating circuit breakers 19A, 19B for protection by performing the above protection control processing based on the received state quantities.
Likewise, a bus wire protection relay 10 is provided to protect the bus wire 17 by activating circuit breakers 19A to 19C to separate the bus wire 17 of the electric power system 15 from the electrical power transmission lines 16A to 16C, and further, a transformer protection relay 1D is provided to protect a transformer 20 by receiving state quantities flowing upstream side and downstream side of the transformer 20 of the electric power system 15 using measurement transformers 18A, 18A and activating circuit breaker 19C, 19D for protection based on the received state quantities.
FIG. 57 is a configuration diagram illustrating an example of an input unit of electric quantities (such as voltages and currents) of the electric power system to each of the digital-type protection control apparatuses. As illustrated in FIG. 57, for example, a voltage which is an electric quantity of the electric power system is detected by the measurement transformer 18B, and the electric quantity at the same portion of the electric power system detected by this single, common measurement transformer 18B is respectively input to multiple digital-type protection control apparatuses 101. The digital-type protection control apparatuses 101 include not only a protection relay but also a monitoring control apparatus, a malfunctioning point locating apparatus, a harmonics measurement apparatus, and the like, and each of the digital-type protection control apparatuses 101 inputs the electric quantity detected by the measurement transformer 18B with the analog/digital conversion unit 2, and the digital operation processing unit 3 performs a relay operation, monitoring control operation, malfunctioning point evaluation operation, high frequency measuring operation, and the like.
The monitoring control apparatus, the malfunctioning point locating apparatus, and the system analyzing apparatus record waveforms of voltages and currents of the system when, e.g., an accident occurs in the electric power system, and uses them for, e.g., consideration of protection relay methods by detailed analysis on the accident phenomenon. Recently, with GPS synchronization, information synchronously measured at many points over a wide region is collected, and phenomena ranging over wide range of the system are measured. It should be noted that FIG. 57 illustrates an example where a voltage of the electric power system is input, but information about a current is also input.
As described above, the reason why a dedicated analog/digital conversion unit 2 is provided for each digital-type protection control apparatus is that each digital-type protection control apparatus is different in the range of analog information (input full scale, frequency band, and the like) and the operation speed required for operation at the protection control target (purpose) of each digital-type protection control apparatus, and it is necessary to optimally design the A/D conversion device 9, the analog filter 6, and the like constituting the analog/digital conversion unit 2.
In this case, there is a harmonics measurement apparatus which is a measurement apparatus relating to the quality of electric power, wherein harmonics are measured by performing A/D conversion on currents and voltages which are input from a CT (current transformer) and a PT (potential transformer) of an electric power system, and an analog filter provided at a stage prior the A/D conversion has frequency characteristics for allowing target harmonic regions to pass through (for example, Jpn. Pat. Appln. KOKAI Publication No. 2002-345172).
However, in the conventional digital-type protection control apparatus, the electric quantity at the same portion of the electric power system is individually input to each digital-type protection control apparatus, and the dedicated analog/digital conversion unit 2 of them each performs input processing, and therefore, when a new digital-type protection control apparatus is applied, it is necessary to develop and install a new analog/digital conversion unit 2 on every such occasion. For this reason, there is a limitation in terms of application, and the economical effectiveness is also deteriorated. Moreover, there is also a limitation in the performance of the analog/digital conversion unit 2 installed individually, and this causes limitations in terms of application.
According to the protection control target (each purpose) of each digital-type protection control apparatus, the performance required by the analog/digital conversion unit 2 is, for example, as follows.
(1) protection relay: large full scale, high speed, stable response
(2) monitoring control: high measuring accuracy at a range close to rating
(3) accident waveform record: high-speed sampling, large full sale
(4) harmonics measurement and voltage sag: high-speed sampling
In other words, in the protection relay, it is necessary to determine an accident by measuring a current and a voltage in a short time from an instance of occurrence of a system accident and give an instruction to a circuit breaker, and in order to measure the current and the voltage at the time when the accident occurs, a large signal full scale (several hundred A or more at the input of the protection control apparatus) is required. In general, as the A/D conversion of the protection relay, a successive approximation type A/D conversion device is used, the sampling frequency of which is around several hundred to several kHz and the resolution of which is around 12 to 14 bits. For example, in general, in order to reduce an error of an operation value of a relay to 5% or less, 40 digits or more are required for relay detection sensitivity. In a case of a 12-bit A/D conversion device, 1 LSB is 1/2048 of a full scale, and in this case, for example, in order to achieve a detection sensitivity of 100 A, the full scale value needs to be about 5000 A. Currently, an A/D conversion device of 16-bit resolution is used in a latest protection relay protecting a trunk transmission power system, but the usable resolution including noise and the like is about 14 bits.
As described above, the protection relay needs to have a design by which the required accuracy can be obtained from the usable resolution of the A/D conversion device. The analog filter 6 requires sufficient attenuation of the sampling frequency in order to prevent an aliasing error of the A/D conversion, and when the sampling frequency is low, particularly steep attenuation characteristics are required. In addition, it is also necessary to have a design that allows for a transient response. In order to obtain stable characteristics, highly accurate devices are required to be used as resistors, capacitors, and the like.
Subsequently, the monitoring control apparatus is required to measure the current and the voltage close to a normal rating (5 A or 1 A) with a high degree of accuracy, and the target measurement error is within 0.1%. Therefore, in general, the monitoring control apparatus uses dedicated full scale input, which is different from the protection relay. In some cases, the malfunctioning point locating system (fault locator) is attached to the protection relay, and uses the same analog input as the protection relay.
The system analyzing system records malfunction phenomena of a system, and is used for, e.g., consideration of a new protection relay method and system operation. The system analyzing system may be incorporated in the protection relay, but in order to observe the details including high frequency, it is necessary to install a dedicated system analyzing system in order. On the other hand, in order to understand phenomena of the electric power system, it is desirable to install them at many locations over a wide range. The harmonics measurement apparatus, which is an apparatus related to the electric power quality, is required to measure high frequency, and is required to measure the 40th or higher harmonic (a frequency 40 times higher than the fundamental wave). Moreover, a high sampling frequency is also needed to detect instantaneous interruption, and the harmonics measurement apparatus uses a sampling frequency of several ten kHz or more, which is higher than that of the protection relay.
As described above, in the electric power system, the analog/digital conversion units 2 specialized in various kinds of digital-type protection control apparatuses are installed. Therefore, when a new digital-type protection control apparatus is applied, it is necessary to develop and install a new analog/digital conversion unit 2 on every such occasion. For this reason, there is a limitation in terms of application, and the economical effectiveness is also deteriorated. Moreover, there is also a limitation in the performance of the analog/digital conversion unit 2 installed individually, and this causes limitations in terms of system application.
Because of such reasons, it is desired to present a technique capable of easily and accurately obtaining A/D conversion data which can be applied to various kinds of digital operation processing.